Purified hydrogen is used in the manufacture of many products including metals, edible fats and oils, and semiconductors and microelectronics. Purified hydrogen is also an important fuel source for many energy conversion devices. For example, fuel cells use purified hydrogen and an oxidant to produce an electrical potential. A process known as steam reforming produces by chemical reaction hydrogen and certain byproducts or impurities. A subsequent purification process removes the undesirable impurities to provide hydrogen sufficiently purified for application to a fuel cell.
In a steam reforming process, one reacts steam and a carbon-containing compound in the presence of a catalyst. Examples of suitable carbon-containing compounds include, but are not limited to, alcohols (such as methanol or ethanol) and hydrocarbons (such as methane, propane, gasoline or kerosene). Steam reforming requires an elevated operating temperature, e.g., between 250 degrees centigrade and 900 degrees centigrade, and produces primarily hydrogen and carbon dioxide, with lesser quantities of carbon monoxide also being formed. Trace quantities of unreacted reactants and trace quantities of byproducts also can result from steam reforming. Efficient operation of the fuel processor requires careful indexing and control of the ratio of water (steam) to carbon-containing feedstock.
The invented system includes a fuel processor that produces hydrogen from a variety of feedstocks. One such fuel processor is a steam reformer, which produces purified hydrogen from a carbon-containing feedstock and water. In the invented system, various mechanisms for controlling the ratio of steam to carbon-containing feedstock are disclosed. In some embodiments, the fuel processing system includes a fuel cell stack that includes at least one fuel cell adapted to produce electrical power from air (oxygen) and hydrogen gas produced by the fuel processor.
Many other features of the present invention will become manifest to those versed in the art upon making reference to the detailed description which follows and the accompanying sheets of drawings in which preferred embodiments incorporating the principles of this invention are disclosed as illustrative examples only.